West Nile disease on ‘a significant upward trajectory’

The virus is new to this continent, and information about it is continuing to evolve.

Manitobans are being warned to protect themselves against mosquito bites, as a sudden upswing in West Nile virus hits people in a broad stretch of Canada running from Alberta through to Quebec. By Aug. 24, nine cases had been reported in Manitoba.

Particularly worrisome outbreaks are occurring in Ontario – where Toronto health authorities had 38 reported cases by late August – as well as, south of us, in Texas’ Dallas County.

Rarer than many mosquitoes here, the Culex picks up the virus from birds.Photo Credit : Jim Gathany

In all, Canada’s Public Health Agency says 62 human cases had been reported in this country up to Aug. 18, and it’s suspected this is, as one expert described it, “only the beginning of a significant upward trajectory in human cases” at summer’s end. The disease is spread by the Culex mosquito, which pick it up from various bird species.

Manitoba Health in an online statement refers to the virus as “an emerging disease”. It is new on this continent and information about its character and behaviour and how to protect and control against it is continuing to evolve. “Ongoing efforts to detect the presence of the virus in mosquitoes and people, combined with information and research from other jurisdictions, will help guide public health recommendations for mosquito control and other actions,” the province’s Health Department explains.

The number of serious West Nile cases in Manitoba has ranged from one to 72 per year since 2003, when the disease was first detected here. The number of West Nile-related deaths has ranged from zero to four.

In the United States, authorities are already calling the outbreak “one of the largest ever seen”. About half the 1,118 cases reported by late August are located in Texas. Dallas County alone had 274 cases, with 11 deaths. Until this year – from 2003 to 2011, Texas had seen only 10 deaths in total.

Heat partly to blame
In both countries, experts are saying the unseasonably hot weather, along with the mild winter and early spring, is partly responsible for the surge in cases. The weather, says one U.S . expert, extended the mosquito season last year, brought the mosquitoes to biting capability earlier, speeded up the multiplication of the virus inside the mosquitoes and drove more birds into populated urban areas in search of water.

The period of highest risk of being bitten by an infected mosquito runs from July to early September, with virus numbers tending to grow as the season progresses. In Manitoba, mosquito traps are monitored through the summer for ongoing information about the risk of the virus.

Most people infected by the virus have no symptoms and don’t become ill. Most of those who become sick have the milder non-neurological syndrome, whose symptoms include fever, headache, fatigue and body ache. The dangerous much rarer West Nile virus neurological syndrome is most likely to attack older adults or persons with pre-existing medical conditions. One of the resulting diseases is encephalitis, an inflammation of the brain, which can have serious complications including paralysis, confusion, coma and even death.

There is no vaccine or special treatment for West Nile virus, and the milder symptoms do not usually require medical care. Anyone with the more serious symptoms are urged to seek medical help.

Mosquitoes get the virus from infected birds, though most birds don’t have the virus even in areas known to be infected. In Manitoba, West Nile virus was first found in birds of the crow family, as well as in horses and mosquitoes the year the virus was first seen here.

Keep body covered
According to the Manitoba Health, the virus was first reported on this continent in 1999, in New York City – which incidentally today has an elaborate, year-round program to monitor for the virus. The virus has now been found in every state of the continental U.S. except Vermont and in much of Canada.

Manitobans are urged to protect themselves against West Nile by minimizing their exposure to mosquito bites: reduce the time spent outdoors between dawn and dusk; apply a mosquito repellent containing DEET; wear light-coloured, loose-fitting clothes with long sleeves and pant legs, and ensure that door and window screens fit tightly.

It is also important to remove mosquito habitats around the home: regularly clean and empty eavestroughs, pool covers and other items that collect water; clean and empty bird baths weekly; cover openings in rain barrels with mosquito screening; cut the grass around your home, trim hedges and trees around doorways and seating areas.

Culex mosquitoes lay their eggs on standing water. The fewer Culex mosquitoes that hatch, says the Health Department, the lower the risk of West Nile virus. Even small amounts of water may produce adult mosquitoes if allowed to stand for a week or more.